1.Field of the Invention
The invention relates to a device for distraction osteogenesis comprising a drive having a lead-screw and two anchors which are displaceable relative to one another by means of the drive, of which one can be connected to a fixed bone segment and one to a movable bone segment.
2.Description of the Prior Art
An area of maxillofacial surgery comprises the reconstruction of bone structures. Such measures are required in a range of illnesses, for example in severe cases of cleft lip, alveolous and palate but also Crouzon or Apert syndrome. The treatment of bone defects after trauma or tumour surgery is also dependent on the reconstruction of bones.
Conventional augmentation methods are based on the transplantation of autologous tissue. Both onlay osteoplasty and the interposition of bone or cartilage tissue are among the methods practiced according to the prior art. In this method, bone fragments are removed from regions of the body lying outside the head and inserted at the defective point in the facial or maxillary area. In the reconstruction of jaws and dentition, the aforementioned measures are usually followed by the insertion of implants.
However, the aforementioned methods have a range of disadvantages and problems, which include, inter alia, slow mineralisation and increased risk of infection of the treated body area, and a comparatively high morbidity of the removal point.
A new process for reconstruction of bone structures has become known under the name distraction osteogenesis. Instead of implantation of tissue, in this process bone tissue is obtained as new. The foundations of this method were laid by the Russian orthopaedic surgeon Ilizarov in 1988, and led to a method for extending tubular bones. This is based on pulling apart a callous formed after corticotomy at a rate of about one millimeter per day. This method activates the bone's powers of self healing, so that new callous tissue is continually produced, and thereby the tubular bone is lengthened.
Distraction osteogenesis has developed in an important therapeutic method in maxillofacial surgery. In particular, it is used for vertically building up toothless or tooth-bearing alveolar process segments and hyperatrophic lower jaws in the front-tooth and side-tooth region, or in the region of the entire lower jaw. In the execution of the aforementioned process, distraction devices are used, whose function is to continually displace a bone segment, which covers the reconstruction area and was previously operatively separated from the remaining bone, with respect to the remaining bone. The permanent displacement of the bone segment thus has the consequence that the callous forming between the sides of the displaced and fixed bone is permanently enlarged, and thereby new bone tissue is obtained. It has been found in practice that the callous is formed more intensively the smaller the distraction steps are, that is to say that it is optimum when the distraction takes place continuously. In addition to the formation of new bone, with this method the associated stretching and reproduction of the surrounding soft tissue (histogenesis) is of great advantage. It contributes substantially to the vitality of the displaced bone segment, and therefore to a reduced risk of infection and to rapid healing.
An important consideration in the development of distractors is their miniaturisation. In the distractors known in the prior art, however, this requirement disadvantageously leads to a mediocre stability of the device and less precise guidance of the anchors, which are displaceable with respect to one another.